The present invention relates to a process for preparing alkylene sulfides by an intramolecular dehydration reaction of mercaptoalkanols in a gaseous phase under the presence of catalysts.
Alkylene sulfides, which have superior reactivity, are useful compounds that are extensively used as manufacturing materials for pharmaceuticals, pesticides, and various industrial chemicals as well as being used as a reactant for sulfur-containing polymers.
Concerning processes for manufacturing alkylene sulfides, U.S. Pat. No. 3,687,976 as well as U.K. Pat. No. 1135800 disclose a process wherein ethylene oxide reacts with carbonyl sulfide or carbon disulfide under the presence of catalysts. However, this process has problems with the toxicity of carbonyl sulfide and carbon disulfide as well as with the low yield of alkylene sulfide as a target product.
Further, U.S. Pat. No. 3,622,597 and J. Chem. Soc. (C), p1252-1256, 1969, disclose a process for preparing alkylene sulfides, wherein a mercaptoethanol is subjected to an intramolecular dehydration reaction in a liquid phase under the presence of a catalyst of sulfuric acid series. However, this process suffers from drawbacks wherein the yield of alkylene sulfide as a target product is low because of a large amount of polymerization by-products; and it is expensive to separate the polymerization by-products from the catalyst after the reaction since the reaction is a homogeneous reaction in the liquid phase. Therefore, it is impossible to put this process into practical industrial use.
Moreover, Netherlands Pat. No. 7001172 discloses a process for obtaining alkylene sulfides through the intramolecular dehydration reaction of mercaptoalkanols in a gaseous phase, which is carried out by using solid catalysts such as titanium oxide, zirconium oxide or niobium oxide. It is described that in accordance with this method, alkylene sulfides can be obtained in a high yield from mercaptoalkanols. However, no description is found in the specification concerning catalyst life, which is a very important factor to stably manufacture the target products, alkylene sulfides. According to examinations carried out by the inventors of the present application, in the case of using the catalysts such as titanium oxide, zirconium oxide or niobium oxide, since the acid property of the catalysts is too strong, so-called coking develops during the reaction such that deactivation of the catalysts proceeds quickly. Moreover, in addition to the quick deactivation of the catalysts, MgTiO.sub.3 and SrTiO.sub.3 that are, disclosed in the above Laid-Open Patent Publication, they have extremely low activity in comparison with such a catalyst as titanium oxide. Therefore, it has been shown that this method using these catalysts fails to provide a satisfactory method from the industrial point of view.